It had been tracing outstanding debtors for a finance organisation and managed to get hold of the addresses of some 250 people as a result of calls to Northern Ireland officials in 2005.

Infofind is based in Kingston in greater London. It was yesterday convicted by Kingston magistrates of 44 breaches of data protection legislation which protects personal information.

Belfast officials tricked by the callers assisted the investigation into the firm by the Information Commissioner's Office (ICO), the UK's data protection watchdog.

The Infofind callers posed as DWP employees and gave false names. The firm used in-house DWP information on computer systems as part of its con.

In January 2005, a Belfast official gave information on eight people over the phone but afterwards filled in a call report, sparking an ICO probe.

In September 2005, calls were made to two Belfast civil servants and information relating to 245 individuals was provided.

The ICO probe found that details disclosed from Ulster related to individuals a finance company hired Infofind to trace. Infofind had a written agreement with this firm, On:Line Finance, to comply with Data Protection.

The prosecution resulted in fines totalling £2,800 for Infofind's MD Nick Munroe, along with a £400 penalty for Infofind itself. They were also ordered to pay £5,000 towards costs.

ICO solicitor Philip Taylor said: "Obtaining and selling personal information is a serious offence which can be highly damaging to the individuals concerned. This prosecution is the result of a thorough investigation by the Information Commissioner's Office and is part of our ongoing work to stop the illegal trade in personal information.

"Individuals must be confident that their personal information is stored securely by those organisations which hold and process it. The ICO is working with the Department for Work and Pensions to provide training for employees on how to deal with these bogus callers."

A DWP spokesman said it took the protection of customer information very seriously.

"Since these incidents occurred, we have reviewed and simplified guidance to staff on protecting customer information against this kind of threat."

Information Commissioner Richard Thomas, has called for prison sentences of up to two years for the illegal buying and selling of personal information.